This invention relates in general to sewing devices and in particular to a new and useful method of manufacturing a hollow needle from a round metal blank to form needles of a kind which is particularly applicable for associating fasteners for tags, buttons and similar items to textile materials or other carriers.
Hollow needles of this kind are employed in devices for attaching buttons, tags, fasteners, etc., to textile materials or similar carriers, which fasteners are made of plastic and serially and detachably fixed to a string. They comprise each a head portion, a piece of filament extending transversely therefrom, and a cross pin provided in the middle or at the end of the filament. The hollow needle serves the purpose of piercing the carrier to which the fastener is to be attached and of passing the cross pin therethrough. To this end, the device is equipped with a piston which is movable in reciprocating motion in the guide channel of the needle, transversely to a feed channel through which the cross pin of the fastener is introduced into the needle to be pushed therethrough.
While manufacturing such hollow needles from round steel in accordance with the prior art, the guide channel is produced by drilling a concentric bore from the front side into the blank rough-turned with a needle point and a mounting shank, which bore extends about to the location where the needle point portion starts to taper. This requires a center bore in advance, in the front face of the mounting shank. Then, the release slot of the bore is milled adjacent the needle point bore end, by means of a disc-shaped cutter having a width exceeding the outer diameter of the needle and introduced radially to a proper depth to produce a recess in the shape of a circular sector, whereupon, by means of another milling cutter having a smaller diameter and a width corresponding to the diameter of the bore, the arcuate, shallowing-out end portion of the bore is milled. Thereafter, with still another disc-shaped milling cutter narrower than the bore diameter, the longitudinal slot within the bore is milled in a further operation.
Even while disregarding the subsequently necessary operation of trimming, five machining operations are thus needed for producing the guide channel alone, with prior art methods.
It is further known to manufacture hollow needles for such tag attaching devices from oblong pieces of flat stock having lateral front end portions for forming the needle point, by bending the blank to a tubular element for guiding the cross pins, in which the longitudinal edges form the longitudinal slot and the projecting lateral rear portions left straight are used for fixing the hollow needle in a housing. The mounting shank at the rear of the needle is then formed by a pointed piece of plastic. The manufacture of such hollow needles formed by bending to a tube is inexpensive indeed, however, they have the disadvantage of an unsatisfactory stability, particularly in the needle point zone, so that they may easily deform or, with hard materials to be pierced, the point may break off or soon become dull (see German AS No. 18 05 474). For this reason, in practice, hollow needles machined from round steel are preferred in the manufacture of tag attaching devices (in this connection see U.S. Pat. No. 2,069,878).